Mechanical Glass Transition Research Articles

The effect of mechanical glass transition temperature on the oxidation rates of omega fatty acids in condensed biopolymer matrices

The concept of glass transition has been used in food products to study their stability, extending shelf life and enhancing organoleptic desirability. This investigation evaluates the effect of three-dimensional structure as a barrier to oxidation of omega fatty acids in condensed hydrocolloid-based matrices. Two high-solid preparations were employed: κ-carrageenan with glucose syrup and genipin-crosslinked gelatin with polydextrose. They supported discontinuous microscopic inclusions of linoleic and linolenic acids within the rubber-to-glass transition region of the condensed mixtures. Glass transition temperatures (Tg) were estimated using differential scanning calorimetry and in-shear dynamic oscillation. The rate of lipid oxidation was monitored by analysing hydroperoxide (ROOH) production during each oxidation phase. The structural transformation of the supporting matrices as a function of temperature significantly affects the oxidation processes. The mechanical or network Tg exhibited higher values than the calorimetric Tg, supporting reduced lipid oxidation rates by suppressing ROOH accumulation in the densified glassy matrices.

Effect of water activity on the mechanical glass transition and dynamical transition of bacteria-solute systems

This study examined the mechanical glass transition and dynamical transition of bacteria (Cronobacter sakazakii)-solute (glycerol and glucose) systems. From the effect of water activity (aw) on the mechanical relaxation, the aw at which mechanical glass transition occurs at 25 °C (a typical ambient temperature) was determined as 0.225 for the glycerol-added sample and 0.540 for the glucose-added sample. These values were lower than that (0.667) reported previously for non-added sample. The effect of temperature on the mean square displacement of atoms within the samples was investigated by incoherent elastic neutron scattering. The aw at which dynamical transition occurs at 25 °C was determined as 0.156 for the glycerol-added sample and 0.475 for the glucose-added sample. These values were lower than that (0.675) reported previously for non-added sample. According to the Couchman-Karasz model, the Tg for the bacteria plasticized by the additive and that for the bulk additive were obtained.

Rheological properties and aging resistance of self‐healing polyurea elastomer modified asphalt

AbstractPolymer modified asphalt containing dynamic chemical bonds has the potential to increase the service life of asphalt pavement due to its excellent self‐healing ability. The effect of this self‐healing accelerator with dynamic chemical bond on the rheological properties and aging resistance of asphalt binder is still unclear. In this study, a self‐healing polyurea elastomer (PUA) modified asphalt containing dynamic disulfide bonds was prepared. The high‐ and low‐temperature performance and fatigue resistance of PUA modified asphalt were studied through multiple stress creep, low‐temperature bending beam rheometer, mechanical glass transition temperature, and linear amplitude scanning tests. Moreover, considering the service environment of asphalt over a wide temperature range (−30–70°C), three rheological aging indices (RAI) were proposed. At the same time, the aging resistance of PUA modified asphalt was evaluated by chemical aging index (CAI) based on carbonyl and sulfoxide groups. Finally, a linear relationship is established between RAI and CAI over a wide temperature range. The experimental results show that self‐healing accelerators can increase the resistance to permanent deformation of asphalt by 47.41% and the fatigue resistance by 88.54%. The S value of PUA modified asphalt decreased by at most 33.21% and the m value increased by at most 35.23% compared with BA at −18°C. Moreover, PUA can improve the long‐term thermal oxygen aging resistance of asphalt binders by at least 38.33% over a wide temperature range.Highlights Rheological properties of self‐healing polyurea elastomer modified asphalt. Aging resistance of self‐healing polyurea elastomer modified asphalt. Proposed rheological aging indices for different temperature ranges. Clarified the correlation between chemical–rheological aging indices.

Glass transition considerations on the oxidation rate of linolenic acid in high solid gelatin/polydextrose systems

Reducing the susceptibility of lipids to the oxidation process remains essential in food processing. In this regard, the present work assesses the role of vitrification in condensed gelatin/polydextrose systems on the oxidation of entrapped linolenic acid. The polymer based matrix was crosslinked with genipin at distinct levels to manipulate the physicochemical properties and glass transition phenomena. The former was assessed with Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), and scanning electron microscopy (SEM). The latter was followed by differential scanning calorimetry (DSC) and small deformation dynamic oscillation in-shear. Hydroperoxide (ROOH) analysis was chosen as an expedient means of monitoring lipid oxidation, which it was performed over an extensive range of temperature (−10 to 50°C) and time (up to 3 days). ROOH development was assayed during the initiation, propagation and termination phase. Data modelling revealed a sigmoidal pattern of ROOH accumulation throughout the entire stage of lipid oxidation. Rate constants obtained in the initiation and propagation phase of oxidation demonstrate that the mechanical glass transition temperature is a critical parameter for the preservation of lipid components in high solid materials.

Effect of water activity on the mechanical glass transition and dynamical transition of bacteria

The purpose of this study was to clarify the glass-transition behavior of bacteria (Cronobacter sakazakii) as a function of water activity (aw). From the water sorption isotherm (298 K) for C. sakazakii, monolayer water content and monolayer aw were determined to be 0.0724 g/g-dry matter and 0.252, respectively. Mechanical relaxation was investigated at 298 K. In a higher aw range of over 0.529, the degree of mechanical relaxation increased with an increase in aw. From the effect of aw on the degree of mechanical relaxation, the mechanical awc (aw at which mechanical glass transition occurs at 298 K) was determined to be 0.667. Mean-square displacement of atoms in the bacteria was investigated by incoherent elastic neutron scattering. The mean-square displacement increased gradually with an increase in temperature depending on the aw of samples. From the linear fitting, two or three dynamical transition temperatures (low, middle, and high Tds) were determined at each aw. The low-Td values (142–158 K) were almost independent from aw. There was a minor effect of aw on the middle Td (214–234 K) except for the anhydrous sample (261 K). The high Td (252–322 K) largely increased with the decrease in aw. From the aw dependence of the high Td, the dynamical awc was determined to be 0.675, which was almost equivalent to the mechanical awc. The high Td was assumed to be the glass-transition temperature (Tg), and anhydrous Tg was estimated to be 409 K. In addition, molecular relaxation time (τ) of the bacteria was calculated as a function of aw. From the result, it is suggested that the progress of metabolism in the bacterial system requires a lower τ than approximately 6 × 10−5 s.

Glass transition effects on the molecular transport of caffeine from condensed k-carrageenan/polydextrose systems

We investigate the effect of added KCl on the glass transition of potassium-κ-carrageenan/polydextrose and molecular transport of caffeine. Samples were prepared with 2% (w/w) κ-carrageenan, 82% (w/w) polydextrose and 1% (w/w) caffeine to a total solids level of 85% (w/w). KCl was added at 0, 50, 100 and 200 mM to induce a dependence of structural properties on the potassium ion concentration. High-resolution spectral data over a wide spectral range for the tertiary system were collected using Fourier transform infrared spectroscopy (FTIR), which were complemented by tangible evidence of its morphology with scanning electron microscopy (SEM). Work then focused on the estimation of the mechanical (Tgm) and calorimetric (Tgc) glass transition temperature using in-shear dynamic oscillation and modulated differential scanning calorimetry (MDSC). Molecular transport of caffeine in the condensed polysaccharide/co-solute system was followed with UV–vis spectroscopy over a wide temperature range (−20 to 30 °C) and modelled with extended diffusion theory. Time-dependent mass transport of the diffusant was correlated to the structural relaxation of the polymeric matrix seen in increasing values of the mechanical glass transition temperature with higher additions of potassium counterions to κ-carrageenan. It was concluded that the mechanical glass transition temperature has a prominent effect on the release kinetics of caffeine in these materials, as compared to the calorimetric glass transition temperature.

Why Does Cronobacter sakazakii Survive for a Long Time in Dry Environments? Contribution of the Glass Transition of Dried Bacterial Cells.

ABSTRACTTo investigate the mechanism of adaptation of Cronobacter sakazakii to desiccation stress, the present study focused on the glass transition phenomenon of dried bacterial cells, using a thermomechanical technique. The mechanical glass transition temperature (Tg) of dried C. sakazakii cells per se, prepared by different drying methods (air drying and freeze-drying) and with different water activity (aw) levels (0.43, 0.57, 0.75, and 0.87), were determined. In addition, we investigated the survival of two strains of C. sakazakii (JCM 1233 and JCM 2127) prepared by different drying methods under different storage temperatures (4, 25, and 42°C) and aw conditions (0.43 and 0.87). While the Tg of the air-dried C. sakazakii cells increased as the aw decreased, the freeze-dried C. sakazakii cells showed an unclear aw dependency of the Tg. Air-dried C. sakazakii cells showed a higher Tg than freeze-dried C. sakazakii cells at an aw of <0.57. Freeze-dried C. sakazakii cells were more rapidly inactivated than air-dried cells regardless of the difference in aw and temperature. The difference between the Tg and storage temperature was used as an index that took into consideration the differences in the drying methods and aw levels. As the difference between the Tg and storage temperature increased to >20°C, the dried C. sakazakii cells survived stably regardless of the drying method. In contrast, when the difference between the Tg and storage temperature was reduced to <10°C, the viable cell numbers in dried C. sakazakii cells were quickly decreased. Thus, the Tg is a key factor affecting the desiccation tolerance of C. sakazakii.IMPORTANCE The mechanical glass transition temperature (Tg) of dried Cronobacter sakazakii cells varied depending on differences in drying methods and water activity (aw) levels. Because the Tg of the dried bacterial cells varied depending on the drying method and aw, the Tg will play an important role as an operational factor in the optimization of dry food processing for controlling microbial contamination in the future. Furthermore, the differences between the Tg and storage temperature were introduced as an integrated index for survival of bacterial cells under a desiccation environment that took into consideration the differences in the drying methods and aw levels. As the difference between the Tg and storage temperature decreased to <10°C, the dried C. sakazakii cells were inactivated quickly, regardless of the drying methods. The relationship between Tg and storage temperature will contribute to understanding the desiccation tolerance of bacterial cells.

Physical and structural characteristics of starch‐based and conventional cookies: Water sorption, mechanical glass transition, and texture properties of their crust and crumb

The physical properties of starch-based cookie (gluten free and low fat) were compared with those of conventional cookie in consideration for the difference between crust and crumb parts. The internal porosity of the samples was measured by X-ray computed tomography. The starch-based cookie had a higher porosity (0.61) than the conventional cookie (0.42). The mechanical glass-transition temperature (Tg ) of the samples was evaluated by the thermal rheological analysis. The anhydrous mechanical Tg of the starch-based cookie was much lower than that of the conventional cookie. The Tg -depression of the starch-based cookie induced by water sorption was more gradual than that of the conventional cookie. For both types of cookie, the crust components were more resistant to water plasticizing than crumb components because of the difference of the equilibrium water contents at each water activity. For the texture analysis of crust components, the whole samples were fractured. The starch-based cookie had a lower fracture force, distance, and energy than the conventional cookie at each water activity point. For the texture analysis of crumb components, a portion of the crust was removed from the whole samples, and the exposed crumb was compressed by a plunger. From the texture profile, a normalized linear length was evaluated. The normalized linear length for the starch-based cookie was higher than that for the conventional cookie. These results were corresponded to the differences in the undeveloped gluten and fat contents.

Stability of vitamin C in broccoli based on the chemical reaction kinetics, micro-region state diagram, and empirical correlations

ABSTRACT Vitamin C degradation of broccoli at different moisture and temperature was measured as a function of storage time and modeled by first-order reaction kinetics. The variation of rate constant was analyzed based on the activation energy, glass transition, BET-monolayer, micro-region state diagram, and empirical correlations. Three domains of chemical reactions were observed as a function of temperature. In the case of broccoli with freezable water (i.e. moist), the first critical temperature (i.e. Tc ) was observed at −20°C (Tc /Tg ′′′: 0.829), which was close to the Tg ′′′ (i.e. experimental ultimate maximal-freeze-concentration glass transition) (−32.2°C); while second critical temperature (i.e. Ts ) was observed at 60.0°C (i.e. Ts /Tg ′′′: 1.383). The activation energy values were 13.6, 75.0, and 43.6 kJ/mole for the phase 1 (moist-glassy), phase 2 (moist-glassy-rubbery) and phase 3 (moist-rubbery-flow), respectively. In the case of frozen-broccoli with un-freezable water, the first critical temperature (i.e. Tc ) was observed at 5°C (Tc /Tgi : 1.021), which was close to the Tgi (onset glass transition) (−0.8°C); while the second critical temperature (i.e. Ts ) was observed at 70.0°C (i.e. Ts /Tgi : 1.260). The second critical temperature was close to the mechanical glass transition temperature. The activation energy values were 13.1, 69.6, and 72.4 kJ/mole for phase 1, phase 2 and phase 3, respectively. Each experimental rate constant was located in the micro-regions of the state diagram. Principal component analysis showed that reaction rates can be grouped into different micro-regions, except one data point in the micro-region 12. This could be due to the wider domain of this region and further sub-micro-regions could be defined. Finally, empirical correlations were developed as dimensionless moisture, temperature, and rate constant, and explored the possibility of developing a generic universal equation.

Swelling behaviour and glass transition in genipin-crosslinked chitosan systems

High-solid chitosan matrices were prepared to investigate the effect of their swelling on structural relaxation and glass transition. Degree of crosslinking in genipin-crosslinked chitosan networks was measured with a ninhydrin assay and a suitable crosslinker concentration was determined for gels used in swelling and thermomechanical analysis. Fourier transform infrared spectroscopy and wide angle X-ray diffraction examined the intermolecular interactions, crystallinity and amorphicity of the biopolymer networks. Swelling characteristics following immersion in water included approximate equilibrium values of the average molecular weight between crosslinks and network mesh size, e.g. 902 g mol−1 and 110 nm for the preparation with an initial solids content of 60% (w/w) after 80 min of swelling, which were quantified with the modified Flory-Rehner theory. Thermal glass transition temperature was observed in the condensed crosslinked networks (≥ 70% w/w total solids) during differential scanning calorimetry experiments. Time-temperature superposition of rheological measurements, obtained with dynamic oscillation in-shear, generated a master curve describing the viscoelastic behaviour of the system, moving through the rubbery, glass transition region and glassy state. Combined analysis using the modified Arrhenius and William-Landel-Ferry theories determined mechanical glass transition temperatures in the range of −68 to −8 °C for the crosslinked biopolymer at intermediate-solid concentrations (40 to 60% w/w solids). An understanding of the effect of swelling on molecular network characteristics was achieved, which is crucial for greater control in the design of systems for the targeted delivery of bioactive compounds.

The Influence of the Geometric Shape of Carbon Nanoparticles on the Strength Properties of Nanocomposite Materials Obtained by Filling an Epoxy Matrix

The effects of filling an epoxy matrix modified with “Viniflex” with carbon nanotubes, fullerene C60, or graphene on the mechanical properties, surface morphologies and glass transition temperatures of the composite materials obtained after curing were studied. It was shown that the largest decrease in glass transition temperature and an increase in impact strength was achieved by the introduction of 0.1 mass% graphene. Filling with graphene and carbon nanotubes increased the bending strength while filling with C60 fullerenes provided the greatest compressive strength and elasticity modulus. An explanation of the results was based on ideas about the relationship of the geometrical shape of the nanofiller to the load direction and features of the phase composition of the composite materials. It is suggested that the carbon nanomaterials had a template effect on the packing of the epoxy matrix chains.

Synthesis and micromechanical properties of graphene oxide-based polymer nanocomposites

The authors have studied the effect of small (≤ 1 wt%) additions of thermally reduced graphene oxide on the microhardness and microindentation kinetics in two types of polymers: polystyrene (i.e. thermoplastic with a glass transition temperature of Tg ≈ 373 K) and polyester resin (i.e. thermosetting plastic, Tg ≈ 300 K). The room temperature creep of nanocomposites under an indenter is described using a three-element rheological Kelvin–Voigt model. The study determines the parameters of this model and how graphene oxide (GO) affects them. In a polystyrene nanocomposite with 0.3 wt % graphene oxide, unrelaxed and relaxed elastic moduli, and the modulus characterizing high-elastic deformation, increase by 11%, 40% and 87%, respectively, as compared to the initial polystyrene; at the same time, microhardness increases by 38% and 45% for the different series of samples. The results obtained indicate that the presence of graphene oxide in the nanocomposite severely restricts the mobility of molecular segments. The addition of 0.3 wt% graphene oxide to polyester resin is accompanied by an increase in the mechanical glass transition temperature of the resin by at least 5 K. This leads to a change in the relaxation state of this polymer: while at room temperature the polyester resin behaves like an elastomer, a polyester resin nanocomposite with 0.3 wt% graphene oxide exhibits glassy properties. At room temperature, the microhardness of polyester resin-glass fabric-graphene oxide nanocomposites with a GO content of 0.5 and 1 wt% increases by 20% and 80% respectively, as compared to that of a polyester resin-glass fabric composite. The authors have obtained the temperature dependences of the microhardness of nanocomposites with a polyester matrix in the range 77–298 K, and have also identified temperature regions where the microdeformation of composites is reversible, which is associated with the formation of crazes with a lower glass transition temperature.

The effect of stabilizing additives on deformation performance of stone matrix asphalt

The goal of the research is to establish the effect of stabilizing additives on a number of deformation and strength indicators responsible for ensuring the durability of stone matrix asphalt (SMA), which are the complex modulus of elasticity, shear stability and bending tension. The modulus of elasticity value measurement was made on KhNAHU’s vibration table using electrodynamic transducer in the temperature range from -20 °C to +50 °C. In the deformation frequency range from 0.01 Hz to 50 Hz, shear stability was estimated by the value of shear limit strength at the temperature of 50 °C on special cylinder samples in conditions of their torsion (simple shear). The bending tension value was estimated on beam sample at different load application rate at the design temperatures of 20 °C, 10 °C and 0 °C. According to temperature dependences of modulus of elasticity, the estimate of SMA physical parameters, such as conditional mechanical glass transition temperature, viscoplastic transition temperature, temperature sensitivity of material and plasticity coefficient, was obtained. The values of shear limit strength with different stabilizing additives (VIATOP, DOLONIT) were obtained. A correlation between shear stability and compressive strength at the temperature of 50 °C was established. Comparison of deformation properties of SMA with asphalt concrete and polymer asphalt concrete using the same consistency of binder was made. The effectiveness of SMA hardening by different stabilizing additives on the basis of temperature dependences of bending strength was determined. The plastic range and temperature sensitivity values of SMA are similar to those of asphalt concrete and polymer asphalt concrete. These parameters are mainly determined by the properties of binder, such as penetration, softening temperature, etc. Polymer asphalt concrete has the highest value of plastic range and the lowest one of temperature sensitivity. The similar patterns are obtained for shear stability. The choice of stabilizing additives affects the deformation-strength properties of SMA. To improve durability of SMA, it is necessary to use polymer modified bitumen

Effects of trehalose and corn starch on the mechanical glass transition temperature and texture properties of deep-fried food with varying water and oil contents

The effects of trehalose and corn starch on the mechanical glass transition temperature (Tg) and texture properties of a deep-fried sample (particles of deep-fried batter) with varying water and oil contents were investigated. Tg decreased linearly with increases in both water and oil contents, attributable to their plasticizing effects. Tg was elevated by the addition of trehalose, likely due to its anti-plasticizing effect. Corn starch had a negligible effect on Tg. The critical water content and water activity (water content and water activity at Tg = 25 °C) were determined by extrapolation, and obtained values were validated by isothermal mechanical relaxation. The texture of the samples changed from brittle to ductile near the critical water content and water activity. The trehalose-added sample maintained a brittle texture at a higher water content than the non-additive and corn starch-added samples, as trehalose elevated the critical water content of the deep-fried samples.

Structural relaxation and glass transition in high-solid gelatin systems crosslinked with genipin

Structural relaxation and glass transition were examined in the swelling behaviour of a high-solid biopolymer matrix; genipin-crosslinked gelatin. Degree of swelling was quantified by the Flory-Rehner theory that furnishes estimates of average molecular weight between crosslinks and network mesh size. Fourier transform infrared spectroscopy and wide angle X-ray diffraction described intermolecular interactions and the extent of amorphicity in the crosslinked matrix. Micro differential scanning calorimetry provided evidence of the changing thermodynamic characteristics of the gelatin network in the presence of the crosslinker. Modulated differential scanning calorimetry and small deformation oscillatory rheology unveiled the vitrification properties of the system. Experimental measurements were treated with the time-temperature superposition principle to unveil an extensive master curve through the rubbery, glass transition and glassy states. Viscoelastic behaviour was modelled with the combined predictions of the modified Arrhenius and William-Landel-Ferry theories to pinpoint the mechanical glass transition temperature that was compared with predictions from calorimetry. Comprehensive understanding of polymeric behaviour during swelling affords greater control in the design of targeted delivery matrices for drugs and other bioactive compounds.

Plasticity of Highly Concentrated Suspensions

The rheological properties of aluminum suspensions in low-molecular-weight poly(ethylene glycol) have been systematically studied within a wide range of concentrations up to the ultimate content of the solid phase (about 70%). As the concentration of dispersed particles is increased, the rheological properties evolve from a Newtonian fluid to an elastoplastic solid. In the region of the flowable state, the studied dispersions have no yield stress. However, above a certain concentration, which is considered to be a mechanical glass transition, the suspensions become non-flowable. At higher concentrations, a region of elastoplastic state of highly concentrated systems arises, which has not yet been considered as we know. The boundaries of this region have been determined and the dependences of the characteristics of elasticity and plasticity on stress have been obtained. This region corresponds to the ultimate degrees of filling and is of importance for contemporary additive technologies and so-called “powder injection molding .”

Effect of glass transition on the hardness of a thermally compressed soup solid

This study described the effect of water content on the glass transition temperature (Tg) of a soup powder and the hardness of a soup solid compressed at various temperatures above and below the Tg. Although differential scanning calorimetry showed indistinct glass transition, thermal rheological analysis revealed a clear mechanical glass transition. The mechanical Tg decreased as water activity (or water content) increased because of a water-plasticizing effect. Since X-ray diffraction showed peaks reflecting crystalline NaCl, lactose, and sucrose, the amorphous region in the soup powder likely consisted mainly of vegetable, yeast, beef, and chicken extracts. The fractural stress of the thermally compressed soup solid increased with water activity of the samples, compressed height (density), and temperature. The results showed that the fractural stress of the soup solid increased dramatically when it was compressed at a temperature above the mechanical Tg.

Effect of water content on the glass transition and textural properties of hazelnut

This study is based on the assumption that the change in the texture of hazelnut, induced by water sorption or desorption, can be derived from the glass transition. No previous study has investigated the glass transition properties of hazelnuts. This study aimed to investigate the effect of water content on the glass transition and textural properties of a roasted hazelnut product. Water content of the sample was adjusted in various relative humidity conditions, and the mechanical glass transition temperature Tg was investigated using thermal rheological analysis (TRA), a type of thermomechanical analysis. The TRA curve exhibited a clear force drop induced by the glass transition, and mechanical Tg of the samples was determined. Water plasticizing effect caused mechanical Tg to decrease as the water content increased. The reduction in Tg was analyzed using the Gordon–Taylor equation and linear equation, and the critical water contents (water content at mechanical Tg = 25 °C) were obtained. The fracturing properties of the hazelnut changed from brittle to ductile at the critical water contents. This suggested that the change in the texture of hazelnut can be characterized by the glass transition.

Mechanical glass transition revealed by the fracture toughness of metallic glasses

The fracture toughness of glassy materials remains poorly understood. In large part, this is due to the disordered, intrinsically non-equilibrium nature of the glass structure, which challenges its theoretical description and experimental determination. We show that the notch fracture toughness of metallic glasses exhibits an abrupt toughening transition as a function of a well-controlled fictive temperature (Tf), which characterizes the average glass structure. The ordinary temperature, which has been previously associated with a ductile-to-brittle transition, is shown to play a secondary role. The observed transition is interpreted to result from a competition between the Tf-dependent plastic relaxation rate and an applied strain rate. Consequently, a similar toughening transition as a function of strain rate is predicted and demonstrated experimentally. The observed mechanical toughening transition bears strong similarities to the ordinary glass transition and explains the previously reported large scatter in fracture toughness data and ductile-to-brittle transitions.

Effects of porous structure and water plasticization on the mechanical glass transition temperature and textural properties of freeze-dried trehalose solid and cookie

This study aimed to examine the effects of porous structure and water plasticization on the mechanical glass transition temperature (Tg) of freeze-dried trehalose solid and cookie. The thermal Tg and mechanical Tg were evaluated by differential scanning calorimetry (DSC) and thermal rheological analysis (TRA), respectively. The mechanical Tg of the porous trehalose sample was slightly higher than that of the pellet sample. The mechanical Tgs for pellet and porous trehalose samples were higher than thermal Tg. Although pellet, crust, and crumb cookie samples showed indistinct glass transition behavior in the DSC thermosgrams, TRA revealed a clear glass transition. There were little differences in the mechanical Tg of the cookie samples. The mechanical Tg decreased with an increase in water content, and mechanically and thermally critical water contents (water content at Tg = 25 °C) were evaluated. Fracture properties of the cookie sample changed discontinuously at the thermally critical water content.